Liquid tension-sensitive valves are used to selectively transmit gas from a gas source to a gas receiver depending upon the tension or energy status of the liquid surrounding the valve. Liquid tension-sensitive valves find wide use in agricultural applications. In such applications, the valve is buried in a planting medium and is used to pass air therefrom to an irrigation actuator as the moisture content of the planting medium decreases. The actuator then causes the medium to be irrigated, whereupon the moisture content thereof increases, which stops the passage of air through the valve and thus the irrigation.
Typical applications of liquid tension-sensitive valves are described in U.S. Pat. No. 3,981,466 (Hunter) and in U.S. Pat. No. 3,758,987 (Crane, Jr.). The Hunter patent utilizes a porous ceramic sensing element or valve at the end of a tube buried in a planting medium. After the medium has been irrigated, the pores of the valve are filled with water and cannot pass air from the ground through the tube to the pressure-responsive actuator controlling the irrigation system. As the soil dries out, the effective pressure of the water within it drops below the atmospheric pressure and the sensing element passes air from the soil to the actuator as soon as the liquid pressure in one of the pores becomes sufficiently negative, relative to the atmospheric pressure, to cause the pore to empty. The air passage initiates the irrigating of the medium which causes it to again return to a moistened state in which the pores of the sensing element are filled with water, thereby preventing the passage of air from the planting medium to the actuator and stopping the irrigation.
In the Crane, Jr. patent, a similar ceramic porous valve or sensing element is inserted into the soil and responds to the moisture of the soil to control the flow of water passing to the soil. When the soil is relatively dry, air flows through the porous element and water is allowed to flow to the soil. When the soil is wet, air cannot pass to the sensing element and the flow of water is terminated.
A basic limitation of the types of liquid tension-sensitive valves described in these prior art patents is that they are designed to receive gas only from the environment in which they are used and are incapable of receiving gas from a source of gas in one environment and transmitting it to a receiver of gas in a different environment solely in response to the liquid content of the environment surrounding the valve. In particular, the sensing devices in the Hunter and Crane, Jr. patents are typically placed near the surface of a planting medium. Irrigation is supplied to the planting medium depending upon the moisture content of the surface region. For thick planting mediums, this results in wasted irrigation insofar as the lower regions of the planting medium, which contain the root structure of the plants, are often still moist when the surface region has dried out and caused the sensor to pass air to an irrigation actuator to initiate the irrigating.
It would be advantageous to place one sensor in the lower portion of a planting medium and have irrigation supplied to the medium only when the lower portion is dry, and also utilize a second sensor or valve in the upper region of the medium to disable the passage of air from the lower sensor (to an irrigation actuator) in response to the moisture content of the upper region to prevent overwatering of the medium. As a result, the lower sensor would initiate the irrigation and the upper sensor would disable the irrigation before the lower sensor became completely moist, thereby allowing the irrigation supplied to the planting medium to gradually progress to the lower portions of the planting medium. Additionally, the upper sensor would prevent the irrigation from occurring if it was sufficiently moist, regardless of the moisture content of the lower sensor. As a result, the irrigation of the medium would be initiated depending upon the moisture content of the lower region and would be stopped or prevented from occurring depending upon the moisture content of the upper region. Therefore, plants would be forced to withdraw any water stored in the planting medium before receiving any more water from the irrigation system. Accordingly, the application of irrigation would be tailored precisely to the water use by the crop.
For such a system to operate properly, air must be passed from the sensor in the lower region through the sensor or valve in the upper region to the irrigation actuator, with the upper sensor only allowing air to pass to the actuator depending upon the moisture content of the upper region. Furthermore, the upper sensor must not itself pass air from the upper region to the irrigation actuator.
As the prior art does not disclose a sensor or valve meeting these requirements, it is the principal object of the present invention to provide a liquid tension-sensitive valve which is either closed or open to the passage of gas therethrough depending upon the tension or energy status of the liquid in the environment surrounding the valve.
It is another object of the present invention is selectively transmit gas from a gas source to a gas receiver in response to the liquid content of an environment different from the environments of the gas source and receiver.
It is yet another object of the present invention to allow two or more liquid tension-sensitive valves to be operated in series to selectively transmit gas from a gas source to a gas receiver.
It is yet another object of the present invention to provide a moisture-sensitive valve for use in an upper region of a planting medium to pass air from a moisture sensor in the lower region of the planting medium to an irrigation actuator to activate irrigation depending upon the moisture content of the lower region of the planting medium and to deactivate or inhibit irrigation depending upon the moisture content of the upper region of the medium.